Transistors, such as metal oxide semiconductor field-effect transistors (MOSFETs), are the core building block of the vast majority of semiconductor devices. Some semiconductor devices, such as high performance processor devices, can include millions of transistors. For such devices, decreasing transistors size, and thus increasing transistor density, has traditionally been a high priority in the semiconductor manufacturing industry.
A FinFET is a type of transistor that can be fabricated using very small scale processes. FIG. 1 is a simplified perspective view of a FinFET 100, which is formed on a semiconductor wafer substrate 102. A FinFET is named for its use of one or more conductive fins (FinFET 100 includes only one fin 104). As shown in FIG. 1, fin 104 extends between a source region 106 and a drain region 108 of FinFET 100. FinFET 100 includes a gate structure 110 that is wrapped around fin 104. The dimensions of fin 104 wrapped by gate structure 110 determine the effective channel of FinFET 100. Fin thickness and length of the effective channel are critical to transistor characteristics. Consequently, the creation of fins having uniform dimensions can be an important aspect of the fabrication process.
FIG. 2 is a simplified perspective view of another FinFET 200; this particular version includes three fins 202 extending between a source region 204 and a drain region 206. As with FinFET 100, a gate structure 208 is formed across the three fins 202. When multiple fins are employed in this manner, it can be extremely important to maintain uniform fin thickness and uniform fin pitch (the distance between two adjacent fins, plus fin thickness). Such uniformity and controllability can be particularly difficult to achieve with conventional FinFET fabrication techniques, especially those that use very small process technologies (e.g., 32 nm or smaller).